The effect of time and input of different amounts of mixing energy on the zeta potential and particle size of an oil-well cement slurry have been studied using an AcoustoSizer. It has been shown that the zeta potential development seems to control the consistency of cement slurries in the early time of hydration. Furthermore, conductivity measurements along with pH and a special particle size distribution measurement has indicated the precipitation of solid fine grain material within the liquid phase at the time the consistency starts to increase. This is at the time the cement slowly starts to thicken and long before the cement sets and starts to solidify.